403A concrete and formwork practice questions.

Five free practice questions on concrete and formwork: block C of the Red Seal 403A Carpenter exam, about 16 of its 100 questions. They are in the exam's format: four options, one correct answer. Answer each one before opening the explanation. No account, no email.

01The questions

1. Procedural · Constructs wall form systems and grade beam formwork

   An ICF foundation wall 2.7 m (9 ft) high is ready to pour. What is the correct placement practice to avoid a blowout of the foam forms?

   1. Place in 1.2 m (4 ft) lifts around the whole perimeter, using a pencil vibrator
   2. Fill each corner to the top first, then fill the straight runs
   3. Skip vibration, since the foam cannot take it and the concrete will self-consolidate
   4. Pour at maximum pump rate so the concrete does not set between lifts
   Show the answer

   A. Correct. ICF manufacturers limit the lift height (commonly about 1.2 m per pass) and have the crew circle the wall so no section carries full height of fluid concrete. A small-diameter (pencil) vibrator consolidates each lift without bursting the forms, and the alignment bracing is installed and checked before the pour.

   Why not the others

   B. Filling to full height in one spot puts full liquid head on the foam and the corners, which are the weakest points. Concrete is placed in lifts around the whole perimeter.

   C. Unvibrated ICF walls honeycomb around the webs and rebar. Internal vibration with a small head is required; external tapping is not enough.

   D. Fast placement raises the lateral pressure and is the main cause of ICF blowouts. Lifts are timed so the lower concrete has started to stiffen.

2. Procedural · Facilitates curing of concrete

   Control joints in a 125 mm (5 in.) slab are to be saw-cut. When should the cuts be made, and how deep?

   1. Within 4 to 12 hours, to full depth so the panels are completely separate
   2. The next morning, to a depth of 10 mm (3/8 in.) so the blade does not hit the mesh
   3. After 7 days, when the slab can take the weight of the saw
   4. Within 4 to 12 hours of finishing, about 30 mm deep (one quarter of the thickness)
   Show the answer

   D. Correct. Shrinkage starts as the slab cools and dries, so joints are cut early: as soon as the concrete is hard enough that the blade does not tear out aggregate, typically 4 to 12 hours after finishing depending on temperature (early-entry saws allow sooner). Depth is one quarter of the thickness, here about 30 mm, enough to create the weakened plane.

   Why not the others

   A. Full-depth cuts destroy load transfer between panels and are unnecessary. A quarter-depth notch is enough to make the crack form at the joint.

   B. 10 mm is too shallow to weaken the slab reliably; cracks will wander away from the joint. Mesh is at mid-depth, well below a quarter-depth cut.

   C. By 7 days most of the early shrinkage cracking has already happened wherever the slab chose. Joints cut late do not control cracks.

3. Procedural · Constructs slab formwork

   A 100 mm (4 in.) slab-on-grade is 12 m (40 ft) long and 6 m (20 ft) wide. Using the rule of thumb that control joint spacing should not exceed about 30 times the slab thickness, how should the joints be laid out?

   1. One joint across the middle, giving two 6 × 6 m (20 × 20 ft) panels
   2. Joints about 3 m (10 ft) apart in both directions, giving roughly square 3 × 3 m panels
   3. Joints 1.5 m (5 ft) apart in both directions so the panels are small enough not to crack
   4. No joints; the slab is small enough to shrink without cracking
   Show the answer

   B. Correct. 30 × 100 mm = 3 000 mm, so joints go at about 3 m: three joints across the 12 m length and one across the 6 m width, producing eight 3 × 3 m panels. Panels are kept close to square (length no more than about 1.5 times width) and joints cut to a quarter of the slab depth.

   Why not the others

   A. 6 m is twice the recommended spacing for a 100 mm slab. The panels would still crack across their middles.

   C. 1.5 m spacing doubles the jointing work for no benefit and produces many more joints to maintain. 30 times thickness is the standard guide.

   D. A 12 m slab will shrink several millimetres and crack where it chooses unless joints tell it where. Unjointed slabs of this size almost always crack.

4. Procedural · Performs basic concrete finishing

   A broom-finished exterior slab has just been screeded. In what order are the remaining finishing operations carried out?

   1. Trowel immediately after screeding while the surface is wettest, then broom the next morning
   2. Float, broom, then bull float to flatten the broom marks
   3. Bull float, wait for bleed water to disappear, edge and joint, hand or machine float, then broom
   4. Broom immediately after screeding so the texture is deepest, then float the edges
   Show the answer

   C. Correct. The bull float is run right after screeding to level and embed aggregate; then the slab is left alone until the bleed water sheen has gone. Edging and jointing come next, followed by floating to compact the surface, and the broom is drawn across last (across the direction of traffic) while the surface is still plastic enough to take the texture. Trowelling is skipped on a broom finish unless a tighter surface is wanted first.

   Why not the others

   A. Trowelling with bleed water on the surface causes scaling and dusting, and by the next morning the surface is too hard to broom.

   B. The bull float comes first, immediately after screeding. Running it after brooming would erase the texture that the finish is supposed to have.

   D. Brooming a just-screeded slab tears the surface and the marks close up as bleed water rises. Brooming is the last operation.

5. Procedural · Constructs column formwork

   Column forms on a slab are being located and plumbed. Which procedure keeps each column at the drawn location and plumb through the pour?

   1. Plumb the form by eye against the adjacent walls and nail a single brace to the slab
   2. Fasten a template to the slab, set the form over it, and brace in two directions
   3. Tie adjacent column forms together at the top so they brace each other
   4. Set the form on the dowels and let the reinforcing steel hold it in place
   Show the answer

   B. Correct. A template (a frame of lumber nailed to the slab around the column outline, at the grid lines) fixes the base; the form is plumbed in both directions with a level or plumb bob and held with braces or pipe braces at roughly 90 degrees to each other. Bracing in one direction only lets the form rack in the other.

   Why not the others

   A. One brace restrains movement in one plane only. Columns need bracing in at least two directions, and plumb is checked with an instrument, not by eye.

   C. Tying forms together lets all of them lean together. Each column is braced independently to the slab or to fixed anchors.

   D. The rebar cage is inside the form and has no connection to it. It does not hold the form in location.

02Answer key

03What block C covers

This block covers concrete work from the excavation up. It includes trench shoring and underpinning, falsework and re-shoring, footing, wall, slab, column and stair forms, ICF walls, form ties and pressure, rebar cover and lap splices, anchor bolts, stripping, placing and vibrating concrete, slump tests, hot and cold weather curing, control joints, finishing, precast units and grout.

The Red Seal Occupational Standard names this block “Performs concrete work”. It carries 16% of the exam, about 16 of the 100 questions, split across two tasks. The share column is each task's weight within the block, as the standard publishes it.

04What the questions turn on

Form pressure and tie spacing

Full liquid head is about 24 kN/m³ times the height of fluid concrete. Cold concrete stays fluid longer and raises the pressure, so slow the pour or add ties. Tie spacing comes from tie load divided by pressure and waler spacing.

Control and isolation joints

Space control joints no more than about 30 times the slab thickness, in near-square panels, and saw them a quarter of the depth within 4 to 12 hours of finishing. Isolation joints separate the slab from walls and columns.

Placing and vibrating

Place in lifts of about 450 to 600 mm with the hose close to the previous lift. Put the vibrator in vertically, about 150 mm into the lift below, and pull it out slowly. Creaking, leaks or bulging mean stop and reinforce.

Curing and finishing timing

Hydration stops once concrete dries out, so keep it moist. In cold weather keep it at 10 °C or above, typically for at least 3 days. Trowelling before the bleed water sheen is gone traps water and air, causing blisters and later dusting.

05The other blocks

The 403A exam has seven blocks. Each has its own page of free questions:

The 403A Carpenter practice exam page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.